Plasma arc cutting is a metal working technique in which the heat required to cut, sever, or perform similar functions on metals is provided by a plasma; i.e. a form in which matter has been heated to an extent and under conditions in which all of the elements are present in ionized or atomic form. In most circumstances, the most efficient way to initiate and generate a plasma is by the application of a sufficient potential difference (voltage drop) between an anode and cathode in the presence of the material from which the plasma is formed, typically a flowing gas. In one form of plasma arc cutting referred to as transferred arc, the potential difference is applied between an electrode in the torch and a metal workpiece itself.
The extreme conditions under which plasmas are formed and maintained are generally harsh on the equipment being used, particularly the torch electrodes. As a result, the torch electrode often includes a small insert of an appropriate metal that is slowly consumed by the plasma. After a certain period of operation, the insert or electrode should desirably be replaced.
In actual use, however, torches are often operated for periods longer than the appropriate lifetime of an insert or an electrode. Under these circumstances, the insert and electrode can suffer a catastrophic failure; i.e. a short circuit or the like in which the large potential difference used to generate the plasma becomes misdirected and severely damages or destroys the operative portions of the torch.
In this regard, those familiar with such torches recognize that they generally include relatively sophisticated gas flow passages in metal parts that direct plasma gases and gas mixtures to the electrode, and often also direct cooling gases--sometimes an alternate flow of the same gas or gas mixture used to generate the plasma--to the torch nozzle and other portions of the torch. It will be readily understood that even partial failure of a torch can easily damage or destroy such passages, resulting in an otherwise useless torch, even if the remainder of the torch escapes damage.
A torch can also be damaged when metal from a cut or weld being carried out by the torch, splashes back upon the torch nozzle. Therefore, to the extent that the splash-back from cutting or gouging operations can be minimized or eliminated, the expected lifetime of the plasma arc torch can be extended.